Mg-Al spinel has been synthesized by using industrial waste from ferroalloy plant, decomposed magnesite and used MgO-C brick as the main raw materials. The influence of decomposed magnesite and used MgO-C brick addition on crystalline structure, micro-morphology and properties of synthesized Mg-Al spinel are discussed. The synthesized product was characterized by XRD and SEM, and the crystallinity of each crystalline phase is calculated by relevant analytical software such as X'Pert plus and so on. The experimental result show the crystalline phase periclase increase with the increasing of decomposed magnesite and used MgO-C brick powder. The crystallinity of crystalline phase is highest when the addition of decomposed magnesite is 40wt%. Activity magnesia generated by decomposed magnesite powder decomposition has helped to improve the crystallinity of Crystalline phase. The energy provided by oxidization of the residual carbon promotes Mg-Al spinel grain growth.